In general, a hydraulic excavator as a construction machine is constituted by an automotive lower traveling structure, an upper revolving structure mounted rotatably on the lower traveling structure, and a working mechanism provided on a front side of the upper revolving structure, capable of moving upward/downward. On the upper revolving structure, a cab, a fuel tank, an operation oil tank and the like are mounted on the front side of a revolving frame, and an engine, a hydraulic pump and the like are mounted on a rear side of the revolving frame.
For the engine of the hydraulic excavator, a diesel engine is used in general. This diesel engine is said to emit harmful substances such as particulate matters (PM), nitrogen oxides (NOx) and the like. Thus, the hydraulic excavator is constituted so that an exhaust gas purifying device is provided in an exhaust pipe forming an exhaust gas passage of the engine. As this exhaust gas purifying device, a PM trapping device having a diesel particular filter (DPF) for trapping particulate matters contained in the exhaust gas and a NOx purifying device for purifying nitrogen oxides (NOx) contained in the exhaust gas are known. Moreover, as the exhaust gas purifying device, a silencer for reducing an exhaust sound volume is also known.
Here, the engine is supported by a vibration isolating mount on the revolving frame. The exhaust gas purifying device is directly mounted on the revolving frame. In this case, a vibration system is different between the engine and the exhaust gas purifying device. Therefore, relative displacement (vibration) between the engine and the exhaust gas purifying device is constituted to be absorbed by a bellows pipe having a bellows shape provided in the middle of an exhaust pipe connecting the engine and the exhaust gas purifying device (Patent Document 1).